The research detailed in this application for the coming year concerns itself principally with mechanisms of cellular immunity. A protein isolated from the sea star Asterias forebesi, sea star factor (SSF), has been demonstrated to simulate many of the effector substances released from immune T cells exposed to specific antigen, and may therefore be used as a probe for T cell function. This protein has a molecular weight of approximately 39,000 daltons and is composed of a single pair of disulfide linked heavy and light chains. The amino acid content of these chains is known, and we have a tentative primary sequence of the first 25 amino acids in the heavy and 21 amino acids in the light chain. We will continue sequence analysis with both of these chains and compare them to known sequence of vertebrate immunoglobulin chains, beta 2 microglobulin, and various of the complement components. The application of SSF to tumor cell cytostasis and cytotoxicity will be studied in experiments utilizing SSF induction of macrophage activity. Recent data demonstrate that SSF activates macrophages through a lymphocyte mediator whose formation is induced by SSF contact with T cells. Macrophages so activated are demonstrably cytostatic to syngeneic tumor cells. We will investigate this interesting finding, using both syngeneic and allogeneic macrophage/tumor cell combinations.